Method and device for controlling the decoding of a LDPC encoded codeword, in particular for DVB-S2 LDPC encoded codewords

Abstract

This is a method for controlling the decoding of a LDPC encoded codeword composed of several digital data, said LDPC code being represented by a bipartite graph between check nodes (CN1) and variable nodes (VNi). Said method comprises updating messages exchanged iteratively between variable nodes (VN1) and check nodes (CN1). Said method comprises, at each iteration, calculating for each variable node a first sum (Λn) of all the incident messages (λi) received by said variable node and the corresponding digital data (λch) and calculating a second sum (VNRnew) of all the absolute values of the first sums (Λn), and stopping the decoding process if the second sum (VNRnew) is unchanged or decreases within two successive iterations and if a predetermined threshold condition is satisfied.

Description

FIELD OF THE INVENTION[0001]The present invention is generally directed to the field of data communication, and more specifically, to the decoding of codewords encoded with an LDPC (Low Density Parity-Check) code.[0002]The present invention is more particularly, but not exclusively, directed to a data communication system utilizing the DVB-S2 (Digital Video Broadcast) standard.BACKGROUND OF THE INVENTION[0003]Low-Density Parity-Check (LDPC) codes were introduced by Gallager in 1962 and rediscovered in 1996 by MacKay and Neal. For a long time they had no practical impact due to their computational and implementation complexity. This changed with advances in microelectronics that led to more computational power available for simulation, and which now enables implementation. Due to their excellent error correction performance they are considered for future telecommunication standards.[0004]An LDPC code is a linear block code defined by its sparse M×N parity check matrix H. It contains ...

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Benefits of technology

[0017]However, if the threshold condition is not satisfied, the decoding process is not stopped even if the second sum is unchanged or decreases within two successive iterations. Such a controlled decoding permits the decoding of an undecodable codeword to be stopped early in the decoding process. A lot of energy and processing time wasted during attempts of undecodable codewords decoding is avoided.

Problems solved by technology

For a long time they had no practical impact due to their computational and implementation complexity.

For decodable blocks or codewords, the stopping criteria taking into account the check node sum of the log-likelihood ratios of the incident edges is a very good stopping criteria, but for undecodable blocks or codewords, the full number of iterations is processed so a lot of energy and processing time is wasted.

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